1. Field of the Invention
The present invention generally relates to polishing optical fibers after they have been leveled, and more particularly, to an apparatus for determining and calibrating the pressure existing between a polishing pad and optical fibers that are being polished to ensure polishing uniformity.
2. Description of the Related Art
Optical fibers are very light, very fragile, and have very small dimensions. During their initial manufacture, there are practical limitations on the lengths of optical fibers that can be drawn. Therefore, the connections between the fibers to create longer designated lengths of fiber are accomplished by splicing. In addition, optical fibers or optical devices must be connected to pieces of terminal equipment, such as optical transmitters and optical receivers, to create functioning optical systems.
The nature of the fibers themselves, both in the material used in their fabrication and in the minute physical dimensions involved, combined with submicron alignment requirements, make connectorization operations difficult. Problems with efficient transfer of energy, minimized optical reflections, and mechanical integrity must be addressed. The complexities of interconnecting the fibers demands careful attention to connector design and a high level of precision in polishing operations.
Optical losses caused by poor connections or poor polishing operations may take many forms. Of course, lateral or axial misalignment of the fibers will cause less than optimal light transfer. Care should also be taken to reduce Fresnel reflection losses, which may be introduced by both the glass-to-air and air-to-glass interfaces if end separation between fibers is excessive. Also, the quality of both fiber ends has an effect on the power coupling. For example, rough or unpolished fiber ends not only contribute to separation losses, they may also scratch or fracture an adjacent polished fiber end. Losses may also occur if the fiber ends lack perpendicularity when joined, which may be caused by uneven polishing. Still other losses may occur where the fiber ends are over polished, thereby producing convex shaped ends that affect the transfer of light.
Before conducting the polishing step, special holding jigs or fixtures, such as the aligning device 100 in FIG. 1, are used in an effort to align or level the fibers relative to each other before contact with a polishing apparatus. As shown in FIG. 1, the fibers 110 are threaded through aligning stems or receptacles 120 so as to protrude below the leveling body 130. Note that the illustrated length of the fiber ends 110a protruding below the leveling body 130 has been exaggerated for clarity. Also, the fiber ends are typically surrounded by a ceramic material for stability and ease of handling.
After the individual fibers are leveled relative to each other, the fiber ends are polished. However, even if the fibers are leveled properly, great care must be taken during the polishing process to ensure the fiber ends are not over-polished or under-polished. As described above, if the fibers experience different polishing rates optical losses may result, which are caused by lack of perpendicularity of the fiber ends, rough edges, excessive separation, or the like.
During a polishing operation, pressure is applied to the polishing pad as it spins or rotates about its own central axis while revolving (i.e., rotating in a circular or elliptical manner) with respect to the leveling device so as to polish the fiber ends. Ideally the leveling device would be maintained in a substantially parallel and horizontal relationship with the polishing pad so that each of the leveled fibers is polished to the same extent with the same pressure. In practice, however, even small mechanical, pressure, and/or alignment inconsistencies cause the leveling device to tilt with regard to the polishing pad, such that the fiber ends experience different polishing rates.
The defective fibers caused by uneven polishing are not discovered until the fibers are tested, which is after the polishing process. If a sufficient number of defective fibers are produced, the polishing machine must be taken off-line so that it can be checked and calibrated. Also, the defective fibers must be re-polished. Such inefficiencies caused by the equipment downtime and the rework of the fibers results in production delays.
Accordingly, there exists a need for a polishing apparatus that can more precisely monitor and adjust the pressure that is exerted by a polishing pad on optical fibers that are being polished to ensure polishing uniformity. There is also a need to monitor the tilt between the leveling device and the polishing pad. Moreover, a need exists for an apparatus for determining and calibrating the actual pressure existing between the optical fibers and polishing pad during the polishing process.